1. Field of the Invention
This invention relates generally to heat sealers and more particularly to heat sealers adapted to seal the mouths of plastic bags.
2. Description of the Prior Art
Plastic bags are used for a great variety of packaging purposes. Properties including low cost, flexibility, transparency, gas and fluid impermeability, thermal stability and sterilizability make them desirable containers for everything from electronic parts to pre-cooked `boilable` foods.
It is often desirable to form an air-tight seal at the mouth of a plastic bag to securely retain the bag's contents and/or to protect the bag's contents against spoilage. A machine known as a heat sealer is typically used to seal the plastic bag by melting a seam between the sides of the bag proximate to its mouth.
A problem with prior art heat sealers is that they are, for the most part, non-portable devices. First of all, they are usually large, heavy devices designed to efficiently seal mass quantities of bags. Secondly, they are almost universally electrically powered, and thus must be used near to an electrical outlet.
In U.S. Pat. No. 3,408,478, J. D. Penn discloses a tool for welding the edges of plastic sheets together. Penn's device is a portable tool including a handle, an elongated heating element having a single loop of resistance wire, and a battery disposed within the handle for heating the resistance wire. The heated wire partially melts the plastic sheets to weld them together.
A possible drawback of Penn's device is that it is battery powered. It is a well documented fact that heat production is one of the most energy inefficient used of electricity, leading to the conclusion that Penn's device would not be able to weld many plastic sheets together before its battery was exhausted.
A number of nineteenth and early twentieth century patents, notably U.S. Pat. Nos. 598,562, 591,677, 337,135 and 1,052,984, describe attachments for kerosene lamps which become heated by the lamp's flame. The attachments are universally used for heating beverages, foods and the like and never addressed the problem of heat sealing plastic bags.
What the prior art fails to disclose, then, is a simple, efficient and portable device for heat-sealing plastic bags.